| View previous topic :: View next topic |
| Author |
Message |
delphy_boy
Joined: 15 Sep 2008
Posts: 8
|
| using the internal oscillator |
 Posted: Fri Feb 20, 2009 11:56 am |
 |
|
Hi,
I am using compiler V4.086 with a PIC18LF6722
I am trying to set the internal oscillator to give a 32MHz clock but am only getting 8MHz. I have tried various options using the built in function setup_oscillator() but none seem to give me this clock rate.
Tried:
| Code: |
#FUSES INTRC
setup_oscillator(OSC_32MHZ|OSC_INTRC|OSC_31250);
setup_oscillator(OSC_8MHZ|OSC_INTRC|OSC_PLL_ON); |
Has anyone any idea? |
|
 |
PCM programmer
Joined: 06 Sep 2003
Posts: 21708
|
|
| Posted: Fri Feb 20, 2009 2:25 pm |
|
|
I don't have that PIC to test in hardware, but I think this program should
work.
| Code: | #include <18F6722.h>
#fuses INTRC_IO,NOWDT,PUT,NOBROWNOUT,NOLVP
#use delay(clock=32000000)
//=============================
void main(void)
{
while(1)
{
output_high(PIN_B0);
delay_ms(500);
output_low(PIN_B0);
delay_ms(500);
}
} |
CCS reads the #fuses and #use delay() statements, and then creates
start-up code to set the correct frequency for the internal oscillator
and also to set the PLLEN bit. I notice you didn't have a #use delay()
statement in your code for 32 MHz. That's essential. Here's part of the
.LST file for the program shown above. This is with compiler vs. 4.085.
| Code: | .................... void main(void)
.................... {
0002A: CLRF TBLPTRU
0002C: BCF RCON.IPEN
0002E: CLRF FSR0H
00030: CLRF FSR0L
00032: MOVLW 70
00034: MOVWF OSCCON // Set INTOSC = 8 MHz
00036: MOVLW 40
00038: MOVWF OSCTUNE // Set PLLEN bit = 1
0003A: MOVF OSCCON,W
0003C: MOVF ADCON1,W
0003E: ANDLW C0
00040: IORLW 0F
00042: MOVWF ADCON1
00044: MOVLW 07
00046: MOVWF CMCON
|
Also, what's the Vdd voltage on your PIC ?
There's a formula in the Electrical Characteristics section of the PIC
data sheet:
| Quote: | | FMAX = (16.36 MHz/V) (VDDAPPMIN – 2.0V) + 4 MHz; |
This works out to a maximum 25 MHz frequency for a 3.3v Vdd. |
|
|
delphy_boy
Joined: 15 Sep 2008
Posts: 8
|
|
| Posted: Sat Feb 21, 2009 2:29 am |
|
|
Thanks PCM programmer,
I will give this a try.
I did have the #use delay statement, i just didn't post it.
Also i have read a few other things that say the oscillator has to be set to the primary if the internal oscillator is to be used at 16 or 32MHz. The in-built functions of the complier do NOT allow for this, nor does the project wizard. In both instances they set the oscillator source to internal which I am assuming will be my problem seen as in your code the value written to the OSCCON register sets the source to primary.
Your right about the Fmax, i forgot about that. I will just have to settle for 16Mhz internal clock instead.
Thanks again |
|
|
|
FAQ 
Search
Register
Profile 
Log in to check your private messages 
Log in
